Muffler



Patented Dec. 12, 1933 UNITED STATES PATENT OFFICE Application September28, 1932 Serial No. 635,264

\ 4 Claims.

' This invention relates to silencers and more particularly to silencersof the recently developed sound wave attenuating type.

There has recently appeared and been marketed a line of silencers havinga plurality of relatively telescoped shells, the inner one of whichprovides, at least in part, a thru passage for the escape of exhaustgases from internal combustion engi'nes. Between the inner shell and thenext adjacent shell, is provided means for attenuating sound waves. Inone construction such means comprises a mass of steel wool or the like,whereas in another construction, developed by applicant, the meanscomprises a series of i annular frusto-conical diaphragms.

In both of these constructions, the inner shell is provided with a largearea covered with a plurality of closely spaced minute perforations thruwhich sound waves pass from the inner shell to so to the space,therearound, in which is disposed the wave attenuating means.

It has been discovered that the presence of these minute perforations,for some reason not at present known to applicant, creates an extremelyobjectionable whistling" noise, and the principal object of theinvention-is to provide means for eliminating such whistling" noiseentirely, or at least, to a large degree.

Other objects of the invention will be readily a0 understood andappreciated upon reference to the following detailed description of anembodiment of the invention and upon reference to the appended drawing,whose Fig. 1 shows an embodiment in longitudinal section, and whose Fig.2 is a section on line 2-2 of Fig. 1, and

whose Fig. 3 is a diagrammatic view. Referring to the drawing, it willbe seen that 40 there'is shown a silencer-including a plurality ofrelatively telescoped shells 10, 11, and 12, having open ends closed byend headers 14 and 15-.

The inner shell is open from header to header to provide a thru passagefor exhaust gases from the inlet header 14 to the outlet header 15 andfor a large area is covered with a plurality of minute, closely spacedperforations 16. These create a communication between the interior ofthe inner shell 12 and the space between the shells 11 and 12, whichspace contains sound wave attenuating means, such as the series ofi'rusto-conical resonator plates '17.

The intermediate shell 11 is provided with large openings 18 and 19which creates communication the interior of the intermediate shell andthe space between it and the outer shell.

If the perforations 16 are formed simply by stamping or cutting them outof the inner shell, then, for some unknown reason, there is created anobjectionable whistling" noise, caused by the passage of sound wavesthru the perforations. In order to eliminate such noises, theperforations are formed in the'crowns of frusto-conical bosses 21 formedfrom the shell 12. This has 66 been found to eliminate the objectionablewhistling noises mentioned above and has been found to be extremelydesirable in silencer construction.

It will be observed that while the perforations 70 16 are shown as beinground and small holes, they might perhaps be in the nature of slots,oblong, oval, etc., or might also be in the form of squared or polygonalholes.

Further, it will be observed that the deflections around theperforations should be great enough so as to prevent any sharp edges, ontheir under surface, being presented to the gases rushing thru the innershell past the perforations, in paths at right angles to the axes ofthese perforations. It is believed that the sharp edges, on the innersurface of the'inner shell, at the perforations, as provided in priorart constructions, causes the sound waves passing thru the perforations,to be split, as illustrated diagrammatically in Fig. 3, with theattendant whistling" noises. In the construction disclosed, the edges ofthe perforations are rounded, as shown, to prevent such splitting ofsound waves.

It will also be observed that the deflected edges at the'perforationsare far more rigid than prior art, undeflected edges, and thatconsequently, they willnot vibrate or become distorted, temporarily orpermanently. This freedom from vibration and distortion is believed tobe an important factor in making the silencer more free from noises thanprior art silencers.

smoothened, and means disposed in the annular no space between the twoshells tor aiding in sound wave attenuation, the extrusions engaging themeans and cooperating to retain them in place.

2. A silencer of the class specified including two relatively telescopedshells, the inner one of which is provided with a plurality of closelyspaced, minute, outwardly extruded perforations having their sound waveentrance edges smoothened, and diaphragms disposed in the annular spacebetween the shells, the extrusions engaging the diaphragms andcooperating to re-. tain them in place. a

3. A silencer of the class specified including two relatively telescopedshells, the inner one of which is provided with a plurality of closelyspaced, minute, outwardly extruded perforations having their sound waveentrance edges smoothened, and means disposed in the annular spacebetween the two shells for aiding in sound wave attenuation, theextrusions engaging the means and cooperating to retain them in placeand also preventing the gathering of soot or the like in theperforations.

45A silencer of the class specified including two relatively telescopedshells, the inner one of which is provided with a plurality of closely

